1. Field of the Invention.
The invention disclosed herein relates to the transdermal administration of medicaments to human and animal subjects. More particularly, the present invention pertains to active iontophoretic delivery systems in which electrical contacts are applied to the surface of the skin of a subject for the purpose of delivering medicament through the surface of the skin into underlying tissues.
2. Background Art.
During active iontophoresis, direct electrical current is used to cause ions of a soluble medicament to move across the surface of the skin and to diffuse into underlying tissue. The surface of the skin is not broken by this administration of the medicament. When conducted within appropriate parameters, the sensations experienced by a subject during the delivery of the medicament in this manner are not unpleasant. Therefore, active iontophoresis presents an attractive alternative to hypodermic injections and to intravascular catheterization.
The direct current employed in active iontophoresis systems may be obtained from a variety of electrical power sources. These include electrical equipment that ultimately receives power from a wall socket, paired regions of contrasting galvanic materials that when coupled by a fluid medium produce minute electrical currents, and consumable and rechargeable batteries.
A flow of electrical current requires an uninterrupted, electrically-conductive pathway from the positive pole of a power source to the other, negative pole thereof. Living tissue is made up primarily of fluid and is, therefore, a conductor of electrical current. In an iontophoretic circuit, the opposite poles of a power source are electrically coupled to respective, separated contact locations on the skin of the subject. The difference in electrical potential created by the power source between those contact locations causes a movement of electrons and electrically charged molecules, or ions, through the tissue between the contact locations.
In an active iontophoretic delivery system, the polarity of the net overall electrical charge on dissolved molecules of a medicament determines the contact location on the skin at which a supply of the medicament of must be positioned. A positively charged medicament in a reservoir against the skin of a patient must be coupled to the positive pole of any power source that is to be used to administer the medicament iontophoretically. Correspondingly, a reservoir on the skin of a patient containing a negatively charged medicament must be coupled to the negative pole of such a power source. Examples of common iontophoretically administrable medicaments in each category of polarity are listed in the table below.
Positive Polarity MedicamentsNegative Polarity MedicamentsBupivacaine hydrochlorideAcetic acidCalcium chlorideBetamethasone sodium phosphateLidocaine hydrochlorideCopper sulfateZinc chlorideDexamethasone sodium phosphateLidocaineFentinolMagnesium sulfateNaproxen sodiumSodium chlorideSodium salicylate
The medicament supply is housed in a fluid reservoir that is positioned electrically conductively engaging the skin of the subject at an anatomical location overlying the tissue to which medicament is to be administered. The medicament reservoir can take the form of a gel suspension of the medicament or of a pad of an absorbent matrix, such as gauze or cotton, which is saturated with fluid containing the medicament. In some instances the fluid containing the medicament is provided from the manufacturer in the absorbent matrix. More commonly, the fluid is added to the absorbent matrix by a medical practitioner at the time that the medicament is about to be administered to a subject.
An iontophoretic circuit for driving the medicament through the unbroken skin is established by coupling the appropriate pole of the power source through the medicament reservoir to the skin of the subject at the anatomical location at which the medicament is to be administered. Simultaneously, the other pole of the power source is coupled to an anatomical location on the skin of the subject that is distanced from the medicament reservoir. The coupling of each pole of the power source is effected by the electrical connection of each pole to a respective electrode. The electrode at the medicament reservoir is referred to as an active electrode; the electrode at the location on the skin distanced from the medicament reservoir is referred to as a return electrode.
The electrical potential that is imposed across the medicament reservoir of an iontophoretic circuit produces electrical current flow by causing electrolysis in some of the molecules of the water (H2O) in the solution in the reservoir. In electrolysis, the positively-charged hydrogen ion (H+) of a water molecule becomes separated from the negatively-charged hydroxyl radical (HO−) of that same molecule. These ions and radicals then migrate in respective opposite directions through the solution in the medicament reservoir. The hydrogen ions (H+) move toward the negative pole of the electrical potential being imposed on the solution, while the hydroxyl radicals (HO−) move toward the positive pole.
The interaction of these migrating ions and radicals with themselves and with other of the chemicals in the solution has a tendency to change the initial hydrogen-ion concentration, or the pH, of the solution in the medicament reservoir. Instability in the pH of the solution in a medicament reservoir raises safety concerns. Any extreme that is allowed to develop in the pH of that solution over the course of therapy, gives rise to the possibility that the medicament reservoir in that condition altered pH condition will produce burns to the skin of the subject at the anatomical location on the skin that is in contact with the medicament reservoir.
The medicament reservoir with an associated active electrode may be conveniently retained against the skin by a first adhesive patch, while the return electrode may be retained against the skin at some distance from the medicament reservoir using a distinct second adhesive patch. Alternatively, the medicament reservoir with the associated active electrode, as well as the return electrode, may be carried on a single adhesive patch at, respective, electrically isolated locations.
The use of iontophoresis to administer medicaments to a subject is advantageous in several respects.
Medications delivered by an active iontophoretic system bypass the digestive system. This reduces digestive tract irritation. In many cases, medicaments administered orally are less potent than if administered transcutaneously. In compensation, it is often necessary in achieving a target effective dosage level to administer orally larger quantities of medicament than would be administered transcutaneously.
Active iontophoretic systems do not require intensive skin site sanitation to avoid infections. Patches and the other equipment used in active iontophoresis do not interact with bodily fluids and, accordingly, need not be disposed as hazardous biological materials following use. Being a noninvasive procedure, the administration of medicament using an active iontophoretic system does not cause tissue injury of the types observed with hypodermic injections and with intravenous catheterizations. Repeated needle punctures in a single anatomical region, or long term catheter residence, can adversely affect the health of surrounding tissue. Needle punctures and catheter implantations inherently involve the experience of some degree of pain. These unintended consequences of invasive transcutaneous medicament administration are particularly undesirable in an area of the body that, being already injured, is to be treated directly for that injury with a medicament. Such might be the case, for example, in the treatment of a strained muscle or tendon.
With some exceptions, no pharmacologically significant portion of a medicament delivered iontophoretically becomes systemically distributed. Rather, a medicament delivered iontophoretically remains localized in the tissue at the site of administration. This minimizes unwanted systemic side effects, reduces required dosages, and lightens the burdens imposed on the liver and kidneys in metabolizing the medicament.
The dosage of a medicament delivered iontophoretically is conveniently and accurately measured by monitoring the amount and the duration of the current flowing during the administration.
Finally, the successful operation of an active iontophoretic system is not reliant on the medical skills of nurses or doctors. Foregoing the involvement of such medical personnel in the administration of medicaments whenever appropriate favors the convenience of patients and reduces the costs associated with the delivery of such types of therapy.